The present invention relates to a seal assembly for a rotary kiln.
Industrial rotary kilns are typically of huge size, up to 100 meters long or more, with a diameter of several meters. Elevated temperatures considerably in excess of 1000.degree. C. are attained therein. The most frequent uses of such kilns are in large cement-manufacturing plants.
Fluidtightness at the ends of the rotating parts of such kilns poses difficult problems, especially at the hotter, lower end. Indeed, it is not only necessary to take into account the temperature conditions at the seal which limits the choice of materials but also considerable displacements due to the expansion of the entire kiln, the atmosphere which is often corrosive and abrasive due to the entrained dust, pressure variations in the kiln which alternately tend to cause discharge of hot gases and intake of air, the phenomena all being detrimental and the main cause of loss of heat.
Heretofore proposed solutions to these problems have been imperfect and failing perfect fluidtightness, one has had to content oneself with limiting the intake of air and hot gas leaks by providing play as small as possible between the rotating and stationary parts.
It has, however, been proposed to eliminate insofar as possible, air intake and gas leaks by using graphite blocks which are maintained by a stationary part and rub constantly against the rotating part. The graphite has good high temperature resistance and a low coefficient of friction.
For example French patent no. 1,438,392 provides a liner formed of a plurality of graphite blocks. Each graphite block is provided with its own force-applying means including a spring, pivots and other elements. But given the great number of graphite blocks employed in practice (e.g. 70) the likelihood of mechanical failure is relatively high.